Electrode for semiconductor device and method for manufacturing same

ABSTRACT

The purpose of the present invention is to obtain an electrode wiring structure for semiconductor devices that can suppress the occurrence of Al voids inside aluminum alloy wiring without regard to the orientation of such aluminum alloy wiring. An interlayer insulator film  11 , a titanium layer  12 , a titanium nitride layer  13  that serves as the barrier layer, an aluminum alloy wiring layer  15  and a protective film  18  are formed on top of the silicon substrate  10  to compose the electrode structure. In this case, a distortion relaxation layer  14 , with a film thickness of approximately over 10 nm and which is an intermetallic compound that includes aluminum and titanium in its composition, is formed in between the titanium nitride layer  13  and the aluminum alloy wiring layer  15 . Because of this distortion relaxation layer, for every wiring width of 1 μm, the number of Al voids with widths of over 0.3 μm is practically reduced to 0.

This is a division of application Ser. No. 08/802,214, filed Feb. 19,1997, now U.S. Pat. No. 6,066,891 which is a continuation of Ser. No.08/431,044 filed Apr. 28, 1995, abandoned.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent applications No. 6-90926 filed on Apr. 28, 1994and No. 6-146289 filed on Jun. 28, 1994, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring electrode for semiconductorsand a manufacturing method thereof. Particularly, the present inventionrelates to a metal system of an electrode which has an aluminum alloywiring layer (hereinafter, referred as an Al alloy layer) and can reducethe defects (called Al void) that occur within Al alloy layers due tothe miniaturization.

2. Related Arts

In recent years, with advancement in technology for integratingelements, technologies for miniaturization and multilayering have becomeessential. As miniaturization advances, the need to design finer widthsfor the wiring in the Al alloy layer arises. But, as shown in FIG. 4, asthe wire widths become finer than 2 μm or 3 μm, especially less than 1μm, Al voids are known to occur inside the Al alloy layer. Such Al voidsare generated as a stress migration due to the tensile stress whichoccurs inside the Al alloy layer during heat treatment. Also, the Alvoids occur when various thin films are multilayered because suchmultilayered structure causes tensile stress inside the element.

If these Al voids become significantly large, the reliability factorbecomes a big problem. For example, the following problems may occur:disconnection of the Al alloy wiring; increase in the wiring resistancedue to the reduction in the cross section of the Al alloy layer;destruction of the elements due to heat generation; delays in theoperation speed; electromigration due to the application of largecurrent and the like.

One conventional method that has been used to reduce the occurrences ofAl void, is to mix copper in the aluminum and silicon (Al—Si) wiringelectrode to form the Al—Si—Cu wiring, wherein the copper acts to hinderthe movement of the Al atoms.

Such wiring electrode is disclosed in JP-A-63-152147. The publicationdiscloses that, if the crystal surface of the Al—S—Cu wiring is orientedat the (111) plane, the occurrence of Al voids is further reduced. Inother words, as the (111) plane is filled most densely with Al atoms,the movement of an Al atom is restrained by the other Al atoms, ormovement of the Al atoms for easing the tensile stress inside the Alalloy layer is restrained, which leads to fewer occurrences of Al voids.

However, the (111) plane orientation of the Al—Si—Cu wiring has a closerelation to the underlying crystal structure. For example, as disclosedin JP-B-3-3395, JP-A-4-42537 and JP-A-3-262127, it has been discoveredthat it is difficult to properly orient the crystal surface of the Alalloy when a metallic nitride film of high melting point, like atitanium nitride (TiN) layer, is interposed under the Al alloy layer asa barrier metal.

Thus, for the wiring electrode disclosed in JP-A-63-152147, theunderlying crystal structure needs to be supervised carefully to improvethe orientation of the Al—Si—Cu wiring, and because of this,improvements in productivity cannot be expected.

SUMMARY OF THE INVENTION

The present invention, which has been done in consideration with theabove problem, aims to provide an electrode structure that can curb theoccurrences of Al voids inside Al alloy layers, irrespective of theorientation of an Al alloy layer which is located over a titaniumnitride layer.

To achieve the above objective, the inventors of the present inventionhave investigated, based on the manufacturing conditions and the like,methods which can curb the occurrences of Al voids in Al alloy layersirrespective of their orientation. From these investigations, it wasdiscovered that the layer formation conditions of the titanium nitridelayer, which was assumed to have no relation whatsoever with theoccurrence of the Al voids, can drastically reduce the occurrences of Alvoids.

The present invention is based on the information gathered by theinventors from the results of their investigations and an electrodestructure according to the invention has the following characteristics:it is constructed on a semiconductor substrate, with an interlayerinsulator film which has an aperture corresponding to a contact area ofthe substrate; a barrier layer, whose composition includes titaniumnitride, contacts the semiconductor substrate via the aperture of theinterlayer insulator film; an aluminum alloy wiring layer is formed overthe barrier layer; and a distortion relaxation layer is formed betweenthe barrier layer and the aluminum alloy wiring layer with a film thathas a thickness of over 10 nm and made up of an intermetallic compound,whose composition includes at least aluminum and titanium.

By placing the distortion relaxation layer with a thick film (10 nm ormore), the distortion, acting inside the aluminum alloy wiring layer, iseased and thus, irrespective of the orientation of the aluminum alloywiring layer, occurrences of Al voids inside the Al alloy wiring layercan be suppressed.

Or, it may be that the present invention has the following features: forevery 1 μm of the line width of the aluminum alloy wiring layer, thethickness of the distortion relaxation layer, which is an intermetalliccompound including aluminum and titanium and which is to be placedbetween the barrier layer and the aluminum alloy wiring layer, is set sothat the Al voids, the width of which is over 0.3 μm, can be effectivelymade zero. In other words, the distortion relaxation layer preferablyhas a thickness which can suppress the occurrence of the Al void thewidth of which is approximately one third or more of the line width ofthe aluminum alloy wiring layer. Such film thickness according to thepresent invention, which was unachievable in the reactant layer formedthrough the reaction of the titanium nitride and aluminum alloy wiringlayers when the conventional method is performed, make it possible toenable the drastic reduction of Al voids.

In addition, it is desirable that the distortion relaxation layer beformed to cover at least 40% of the interface between the barrier layerand the aluminum alloy layer.

Moreover, the distortion relaxation layer can either be a Al₃Ti layer oran intermetallic compound that contains Al₃Ti. Ti contained in thetitanium nitride layer can enter between the aluminum lattices andconstitute the distortion relaxation layer of Al₃Ti or an intermetalliccompound containing Al₃Ti, the distortion due to the tensile stress thatoccurs inside the aluminum alloy wiring layer is eased. Consequently,irrespective of the orientation of the aluminum alloy wiring layer, theoccurrences of Al voids inside Al alloy layer can be suppressed.

Furthermore, it is desirable that the oxygen levels at the inside of thebarrier layers and at the interface of the barrier layer and thedistortion relaxation layer be under 1 at %. Because of such, it wouldbe easier for aluminum (Al) and titanium (Ti) to react to each other.

Moreover, by providing an alloy spike preventive layer between thebarrier layer and the semiconductor substrate, the occurrences of Alvoids can be curbed while at the same time suppressing the occurrence ofalloy spikes. For this case, the first titanium nitride layer ispositioned as the barrier layer and a second titanium nitride layer,with different matter properties from the first one, is placed as thealloy spike preventive layer. With this kind of structure, titaniumnitride layers made of the same material can be used to suppress theoccurrences of both Al voids and alloy spikes at the same time.

Next, a manufacturing method according to the present invention, formaking a wiring electrode basically has the following steps: a step offorming an interlayer insulator film on a semiconductor substrate; astep of forming an opening on the interlayer insulator film whichexposes the surface of the substrate; a step of forming a first titaniumnitride layer on the interlayer insulator film such that the firsttitanium nitride layer contacts the surface of the substrate via theopening; a step of forming an aluminum alloy wiring layer on the firsttitanium nitride layer; and a step of performing a heat treatment afterthe formation of the aluminum alloy wiring layer. In this arrangement,the manufacturing method according to the present invention is furthercharacterized in that: the step of forming the first titanium nitridelayer is carried out through reactive sputtering, wherein titanium istargeted inside the sputtering device supplied under nitrogen gas andwith the condition that the DC power density is 5.5 W/cm² or less; andfurther, the steps for forming the first titanium nitride layer and thealuminum alloy wiring layer are continuously performed while maintaininga vacuum.

By forming the first titanium nitride layer with the DC power densitybelow 5.5 W/cm² and at the same time, performing the formation of thefilms of the first titanium nitride and aluminum alloy layerscontinuously inside a vacuum, reaction between the first titaniumnitride and aluminum alloy layers would be promoted and thus, adistortion relaxation layer with a thick film can be realized.

Also, for the first titanium nitride film obtained immediately after thefilm formation, it is desirable for it to have a resistivity of from 180μΩcm to 1,000 μΩcm and to have a compressive stress of from 0 to 90 MPa.

Furthermore, by only adding a step of forming a second titanium nitridelayer, which prevents alloy spikes, over the surface exposed in theopening of the interlayer insulation film before the formation of thefirst titanium nitride layer, the occurrences of Al voids and alloyspikes can be suppressed simultaneously as explained above. In thiscase, because both the first and second layers are made of the sametitanium nitride material, the manufacturing steps thereof can besimplified.

Moreover, it is desirable that the step of forming the second titaniumnitride layer be formed using a reactive sputtering method performedsuch that the DC power density inside the sputtering device is set over6.96 W/cm². By forming the second titanium nitride layer in this manner,the second titanium nitride layer can be made to function as an alloyspike preventive layer which further reduces the occurrences of alloyspikes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and characteristics of the presentinvention will be appreciated from a study of the following detaileddescription, the appended claims, and drawings, all of which form a partof this application. In the drawings:

FIG. 1 is a cross-sectional view of an electrode structure for wiringaccording to a first embodiment of the present invention;

FIGS. 2A to 2E are cross-sectional views respectively showing theundergoing electrode structure at the different major manufacturingsteps;

FIG. 3 is a graph showing the relationship between the conditions forthe film formation of the titanium nitride layer and the occurrence ofAl voids;

FIG. 4 is a view showing the electrode with an Al void, together with anindication of the width of the Al void;

FIG. 5 is a graph showing an analysis of the composite distribution,obtained through an Auger Electron Spectroscopic device, of a wiringelectrode with Al voids;

FIG. 6 is a graph showing an analysis of the composite distribution,obtained through an Auger Electron Spectroscopic device, of the wiringelectrode in FIG. 1;

FIG. 7 is a graph showing a X-ray diffractometry results of the wiringelectrodes;

FIG. 8 is a diagram showing the wiring electrode with Al voids asobserved through a cross-sectional transmission electron microscopy;

FIG. 9 is a diagram showing the wiring electrode of FIG. 1 as observedthrough a cross-sectional transmission electron microscopy;

FIG. 10 is a graph showing the relationship of the occurrence andnon-occurrence of Al voids with the occupation ratio of the intermediatelayer which acts as the distortion relaxation layer;

FIG. 11 is a view showing the definition of the occupation ratio of FIG.10;

FIG. 12 is a graph showing analysis results of the titanium nitridelayers obtained through X-ray photoemission spectroscopy, which showsthe chemical shift that represents the chemical bonding state ofTi2p_(3/2);

FIG. 13 is a graph showing intensities investigated the Al(111) plane ofthe wiring electrodes by a X-ray diffractometry;

FIG. 14 is a graph showing the relationship between the X-raydiffraction intensity for the Al(111) plane of the wiring electrode andthe annealing temperature;

FIG. 15 is a graph showing the relationship between the X-raydiffraction intensity for the Al₃Ti(202) plane and the annealingtemperature;

FIG. 16 is a diagram showing the structure of the sputtering device;

FIG. 17 is a schematic sectional view showing an occurrence of an alloyspike;

FIG. 18 is a cross-sectional view of a wiring electrode according to asecond embodiment of the present invention;

FIGS. 19A to 19C are cross-sectional views of the wiring electrode ofFIG. 18, each showing a view at a major manufacturing step;

FIG. 20 is a diagram showing the comparison between the secondembodiment and examples 1-3 as evaluated on the Al void density andleakage current;

FIG. 21 is a schematic view showing the structure for measuring theleakage current;

FIG. 22 is a X-ray diffraction diagram of the titanium nitride layerswhen varying power density during the formation thereof;

FIG. 23 is a characteristic diagram showing the relationship of thepower density with the leakage current;

FIGS. 24A and 24B are graphs each showing an analysis of the compositedistribution, obtained through an Auger Electron Spectroscopic device,of a wiring electrode, wherein FIG. 24A shows a case that an alloyspike-preventive titanium nitride layer is formed as a barrier layer andFIG. 24B shows a case that an Al void-preventive titanium nitride layeris formed as a barrier layer;

FIG. 25 is a graph showing the occurrence of leakage currents when thefilm thickness of the first and second titanium nitride layers arevaried; and

FIG. 26 is a graph showing the occurrence of Al voids when the thicknessof the first and second titanium nitride layers are varied.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

(First Embodiment)

FIG. 1 is a cross-sectional view of the semiconductor device that hasthe electrode structure according to the first embodiment and shows thesurrounding area of a contact hole 17. Formed on a silicon(semiconductor) substrate 10 are an interlayer insulator film 11, whichhas apertures as the contact hole 17, and a titanium layer 12. Atitanium silicide layer 16 is formed between the titanium layer 12 andsilicon substrate 10. Also, on top of the titanium layer 12 and thetitanium silicide 16, a titanium nitride layer 13 as a barrier layer isformed, and further, an Al alloy layer 15 composed of Al—Si(1.0 wt%)—Cu(0.5 wt %) and a protective film 18 of an insulating film areformed thereabove.

To make this kind of wiring electrode, after forming the titanium layer12, the titanium nitride layer 13 and the Al alloy layer 15 on top ofthe silicon substrate 10, an annealing process is performed to reducethe resistance of the contact area of the substrate with the electrodesystem, and after which, the protective film 18 is formed. Here, the DCmagnetron sputtering device shown in FIG. 16 is used in forming thetitanium layer 12 and titanium nitride layer 13. That is, argon (Ar) gasis supplied inside the chamber of the sputtering device, and voltage isapplied between the Ti target and the heater. In this way, the Titargets are sputtered by the Ar ions and Ti film is deposited on thewafer (substrate). If nitrogen gas reactant, N₂, is introduced while Tiis being deposited, the nitrogen will react with the Ti to thereby formTiN on top of the substrate.

Here, the inventors varied the conditions, which are the DC powerdensity (obtained by dividing the electric power applied between the Titarget and the heater with the Ti target's area) and the heatertemperature during the film formation of the TiN (referred to assubstrate temperature), for the film formation of the TiN to observe andexamine the occurrences of Al voids. The results of their study areshown in FIG. 3. In FIG. 3, the ◯ symbol refers to the sample with analuminum wiring width of 1 μm in which Al voids the widths of which areover 0.3 μm were not discovered. On the other hand, the X symbol refersto the sample with aluminum wiring width of 1 μm in which Al voids thewidths of which are over 0.3 μm were discovered. Here, Al void width isdefined in FIG. 4. From the relationship shown in FIG. 3, theoccurrences of Al voids are remarkably reduced for the region below thesolid line marked as the border in the graph. Particularly, it must benoted that when the DC power density is 5.5 W/cm² or below, theoccurrences of Al voids can be restrained, regardless of the substratetemperature during the TiN film formation.

Examining the above, when forming a wiring electrode, titanium diffusesfrom the titanium nitride layer to the Al alloy layer during theannealing process (400° C.-480° C.), which is performed to reduce theelectrical connection resistance after formation of the Al alloy layer,or during heat treatment (300° C.-480° C.), which is performed duringand after the formation of the protective film, and thereby thefollowing reaction occurs to form an intermediate layer.

Al+TiN→AlN+Ti  (1)

Ti+xAl→TiAl_(x)  (2)

(Here, x refers to an arbitrary number.)

Because of the occurrence of the reactions shown in equations (1) and(2), a Ti diffusion layer (referred to as the distortion (or stress)relaxation layer) is formed inside the Al alloy, and with such, it canbe thought of that distortion inside the Al alloy is relaxed and thatthe formation of Al voids is suppressed.

In other words, in FIG. 1, annealing the titanium nitride layer 13 andthe Al alloy layer 15 results in the reduction of TiN by Al and theproduction of Ti. This Ti diffuses inside the Al alloy layer 15 in sucha manner that the distortion inside the Al alloy layer is scattered andthus from this, it can be thought of that the distortion relaxationlayer 14 is formed. That is, if there is distortion inside the Al alloylayer due to tensile stress, the diffused Ti enters the spaces betweenthe Al lattices and widens such spaces to relax the distortion and thusform the distortion relaxation layer 14. Because of this distortionrelaxation layer, distortion is relieved and, as a result, theoccurrence of Al voids inside Al alloy layer 15 is suppressed,regardless of the orientation of the Al alloy layer 15.

While it is known that the Al voids are the result of stress inducedmigration which occurs when tensile stress, during the heating process,is applied to the inside part of the Al alloy, the mechanism describedabove for suppressing the occurrences of Al voids works when Ti scattersfrom the titanium nitride layer 13 to the Al alloy layer 15 and forms adistortion relaxation layer 14, which relaxes the tensile distortioninside the Al alloy layer and thereby suppresses the occurrences of Alvoids.

The distortion relaxation layer 14 must have a sufficient thickness tosuppress the occurrences of Al voids. If the electrode has a TiN/Alstructure, the reaction described above is thought to occur because ofthe annealing process after the deposition of Al. While that is thecase, it can be inferred that the film layer, produced by the reaction,cannot function well as a distortion relaxation layer if it is a thinone. In short, even if the diffusion of Ti to the inside part of Alalloy layer occurs, if the layer produced by the reaction is very thin,then such layer is not such one that can suppress the occurrences of Alvoids. This matter can be ascertained from the analogy of the results inFIG. 3. As shown in FIG. 3, even for the same film formation structure,there are differences in the occurrences of Al voids. It can be thoughtof that this is due to the fact that the thickness of the diffusionlayer, caused when Ti is diffused to the inside of the Al alloy layer,differs with the varying conditions of forming the TiN film.

The inventors, using the Auger Electron Spectroscopic device, analyzedthe respective compositions of the samples on which Al voids occurredand the samples on which Al voids were suppressed. FIGS. 5 and 6 showthe analysis results focusing along the depth of the part where theinterlayer insulator film is formed. Both profile in FIGS. 5 and 6 showthe composition along the different depths together with thedistribution of the component elements after annealing which isperformed after the film formation of the Al alloy. FIG. 5 shows theexamination results for those samples marked as X in FIG. 3 while FIG. 6shows the results for those samples marked as ◯ in FIG. 3. Compared tothose samples shown in FIG. 5 which had Al voids, the samples, shown inFIG. 6, which suppressed the occurrences of Al voids, had a Ti diffusionlayer acting as a distortion relaxation layer inside the Al alloy. Theseproduced Ti diffusion layers were confirmed to have considerablethickness.

Thus, if the diffusion layer formed when Ti diffuses to the inside partof the Al alloy layer is very thin, then, as in the samples marked as Xin FIG. 3, Al voids will occur. From this result, the distortionrelaxation layer 14, per 1 μm of the wiring width, has to have athickness that reduces the over 0.3 μm widths of Al voids to practicallyzero. In other words, the distortion relaxation layer 14 has to have athickness that reduces the Al voids, the width of which are over ⅓ aslarge as the width of the wiring, to practically zero.

Also, as in the past, to prevent the elements of the Al alloy(Al,Si,etc.) from passing through the barrier metal (so-called alloyspike), the TiN film is exposed to the atmosphere after formation andheated and treated so that oxygen will be contained in the crystal grainboundaries. The inventors have also confirmed the numerous occurrencesof Al voids in a case where an Al alloy layer is formed after exposingthe formed titanium nitride layer to the atmosphere. This is probablybecause the oxidation of the surface of the titanium nitride layer hasmade it hard for the reaction stated before to occur and thus Ti was notable to diffuse inside the Al alloy. Therefore, as the inventors havedetected, it is important to not include oxygen during the formation ofthe titanium nitride layer and to not expose it to the atmosphere afterthe formation of TiN but rather, the process of film formation should bedone continuously inside a vacuum.

As shown in FIGS. 5 and 6, oxygen was not detected in the interior ofthe Al alloy and titanium nitride layers, as well as in the interfacetherebetween. This is the difference with the usual manufacturingprocesses and is due to the fact that the titanium nitride layer is notexposed to the atmosphere after the film formation thereof. Oxygendetected inside the interlayer insulator film, the titanium layerinterface between the titanium nitride layer and the titanium layer, wasdue to the presence of SiO₂ inside the interlayer insulator film.

X-ray diffractometry was also performed on these samples and as shown inFIG. 7, a broad peak, which indicates the compound TiAl_(x) whose maincomponent is TiAl₃, was detected around the area at which the detectedangle 2θ is 39.3°. Furthermore, it was discovered that this peak appearsmore remarkably for those samples which suppressed Al voids than thosesamples where Al voids occurred. Therefore, from the results shown inFIGS. 3, and 5-7, it is clear that the intermetallic compound layerbetween the aluminum and titanium metals, formed by the diffusion oftitanium to the inside part of the Al alloy from the titanium nitridelayer, suppresses the occurrences of Al voids.

FIGS. 8 and 9 show traces of images of the cross-sectional views of thefilm of the materials where Al voids occurred (the samples marked as Xin FIG. 3) and where such voids' occurrences were suppressed (thesamples marked as ◯ in FIG. 3), respectively, as observed from atransmission electron microscope. In the material where Al voidsoccurred, it can be confirmed from FIG. 8 that a layer (referred to asthe reaction layer to distinguish it from the distortion relaxationlayer stated above) having a thickness at around 7 nm was formed betweenthe Al alloy layer and the titanium nitride layer. On the other hand, asshown in FIG. 9, for the material which suppressed the occurrence of Alvoids, a distortion relaxation layer, which is clearly thicker than thatin FIG. 8, with a thickness of 10 nm was formed between the Al alloylayer and titanium nitride layer. Therefore, if the distortionrelaxation layer 14 has a thickness of 10 nm or more, it is follows thatthe distortion brought about by the tensile stress inside the Al alloycan be eased enough so that the occurrence of Al voids can be suppressedsufficiently.

Furthermore, the inventors used a transmission electron microscope todetermine the proper occupation rate of the distortion relaxation layer,that is to be formed, at the interface of the Al alloy layer andtitanium nitride layer. FIG. 10 shows the relationship of the occupationrate at the interface of the Al alloy and titanium nitride layers of thedistortion relaxation layer with the presence/non-presence of Al voids.The occupation rate of the distortion relaxation layer, R, is defined asfollows: $\begin{matrix}\begin{matrix}{R = {\sum{l_{i}/L}}} \\{= {{\left( {l_{1} + l_{2}} \right)/L} \times 100\quad (\%)}}\end{matrix} & (3)\end{matrix}$

Wherein l_(i) (such as l₁, l₂ in FIG. 11) represents a length of eachdistortion relaxation layer and L represents total length of theinterface between the Al alloy and titanium nitride layers as shown inFIG. 11. It must be noted here that l₁ and l₂ represent the lengths ofeach of the islands of the distortion relaxation layer, if it isscattered at the interface between the Al alloy and titanium nitridelayers (refer to FIG. 11).

From FIG. 10, if the distortion relaxation layer covers more than 40% ofthe interface, it can be found that it can suppress the occurrences ofAl voids.

To make clear the differences between the conditions that make Al voidshappen with those conditions that suppress the occurrence of Al voids,as shown in FIG. 12, the sample that formed only the titanium nitridefilm was measured through X-ray photoelectron spectroscopy (XPS) withthe amount of shift (chemical shift) in the binding energy for theelectron in the Ti2p_(3/2) level of the atom in the Ti, that is intitanium nitride (formed by the chemical bonding of Ti with nitrogen),and was also investigated. For the condition in which Al voids occurred,the chemical shift of the Ti2p_(3/2) in the titanium nitride layer was1.51 eV while the chemical shift in the titanium nitride layer for thecondition that suppressed the occurrence of Al voids was smaller at 1.32eV. The latter implies that the bonding state of nitrogen and titaniumwas weak and thus, it was easier for the titanium from the titaniumnitride to diffuse into the Al alloy layer.

Furthermore, there is another way of evaluating the state of thetitanium nitride layer. For example, forming titanium nitride in thesame conditions as those for the samples marked X in FIG. 3 in which Alvoids occurred, their resistivity after film formation was around 80μΩcm-170 μΩcm.

On the other hand, the resistivity for the titanium nitride, measuredafter its formation under the same conditions as those for the samplesmarked Ω in FIG. 3, was 180 μΩm-1,000 μΩm. In addition, measuring thefilm stress of the titanium nitride immediately after the filmformation, the compression stress of the sample, formed in theconditions that made Al voids occur, was at a high of over 100 MPa,while the compression stress for the sample formed under the conditionsthat suppressed the occurrence of Al voids was relatively lower at 0-90MPa. From this, it can be inferred that the titanium nitride raisedunder conditions below the boundary line in FIG. 3 has a relativelycoarse film with a weak bond state for nitrogen and titanium and thattitanium in titanium nitride diffuses more easily into the inside partof the Al alloy layer.

In the past, generally, Al voids have been thought to be suppressed inthe following way. In other words, for example, as shown in the metalwiring structure disclosed in JP-A-63-152147, it was thought that it wasnecessary for the crystal face of the Al—Si—Cu wiring to be oriented atthe Al(111) plane. This method aimed to reduce the number of defects anddistortions inside the interior of the Al—Si—Cu wiring and in doing so,suppress the occurrences of Al voids. However, the inventorsinvestigated on the samples shown in FIG. 3 and performed Al alloy X-raydiffractometry on them and found out that the samples that suppressed Alvoids and those wherein Al voids occurred were both oriented at theAl(111) plane and moreover, as shown in FIG. 13, in contrast to theprevious proposals, the diffraction intensity was smaller for the samplethat suppressed the occurrence of Al voids. Therefore, afterexamination, the inventors found out, as nobody ever did before, thatthe Al(111) orientation was not the main condition in suppressing theoccurrence of Al voids.

The diffraction intensities for the Al(111) and the Al₃Ti(202) planesfor the different annealing temperatures are shown in FIGS. 14 and 15,respectively. As the annealing temperature gets higher, the diffractionintensity for Al₃Ti(202) plane, formed when Ti from titanium nitridelayer is diffused into the Al alloy layer, gets higher, while thediffraction intensity for the Al(111) plane decreases. From this, forthe sample that has the layer that contains Ti which diffused from thetitanium nitride layer into the Al alloy layer, i.e., for the samplethat suppressed Al voids, it was clear that the Al(111) planeorientation is smaller and that improving the orientation of the Al(111)plane would not suppress the occurrences of Al voids.

In addition, as indicated in FIG. 15, to encourage the production ofAl₃Ti, which becomes the distortion relaxation layer 14, the annealingtemperature applied to the Al alloy layer 15 after film formation shouldbe above 350° C. and is much better if it is set above 420° C. This isbecause of the fact that under 350° C., the X-ray diffraction intensityof the intermetallic compound of Al and TiN was not detected and thatthe diffraction intensity of the same increased rapidly if the annealingtemperature was over 420° C.

Next, a concrete example of this embodiment is explained below.

In FIG. 1, the interlayer insulator film 11 and the titanium layer 12are formed on top of the silicon substrate 10, with a titanium silicidelayer 16 formed between the titanium layer 12 and the silicon substrate10. Moreover, the titanium nitride layer (barrier layer) 13, the Alalloy layer 15 composed of Al—Si(1 wt %)—Cu(0.5 wt %), and theprotective film 18 made up of an insulator film, are formed on top ofthe titanium layer 12. Also, the distortion relaxation layer 14, whichis an Al alloy layer that contains the diffused Ti, is formed at theinterface of the titanium nitride layer 13 and the Al alloy layer 15.

Next, FIGS. 2A through 2E are used to explain the method formanufacturing the semiconductor device shown in FIG. 1. First, as shownin FIG. 2A, the interlayer insulator film 11, such as PSG (phosphoricsilicate glass) is formed using a CVD (Chemical Vapor Deposition) orsputtering method, and, as shown in FIG. 2B, a contact hole 17 is formedthrough photolithography to expose the surface contact area of thesilicon substrate 10.

For the process shown in FIG. 2C, using the sputtering device shown inFIG. 16, a 20 nm thick titanium layer 12 is formed by sputtering, a 80nm thick titanium nitride layer 13 is formed by the reactive sputteringof Ti inside an atmosphere of a mixture of argon and nitrogen, and a 450nm thick Al alloy layer 15 made up of Al—Si(1 wt %)—Cu(0.5 wt %) isformed by sputtering. These layers are formed continuously and portionsof them are connected electrically to the surface contact area of thesilicon substrate 10. While performing the above sputtering processes,the titanium layer 12, titanium nitride layer 13 and Al alloy layer 15are not exposed to the air and are formed continuously inside a vacuum.Therefore, the inside parts of these layers and their interfacesvirtually do not contain oxygen with the oxygen concentration at below 1at %.

The effective substrate temperature is set at a certain value during theformation of the titanium layer 12, the titanium nitride layer 13 andthe Al alloy layer 15. Since the titanium nitride layer 13 is formed bymaking titanium react in a plasma with a N₂—Ar atmosphere, theconditions for forming the film, such as the effective substratetemperature, the film formation pressure, the ratio of the flow rates ofN₂—Ar gases, the DC power density or the like, will slightly affect thechemical composition ratio, the crystal structure and the degree ofdiffusion of titanium from the titanium nitride layer 13 into the Alalloy layer 15. Because of this, the substrate temperature, the filmformation pressure, the ratio of the flow rates of the N₂—Ar gases andthe DC power density have been set to 300° C., 5.5 mTorr, 1:1 and 4.4W/cm², respectively, in this embodiment.

After formation of the Al alloy layer 15, the titanium layer 12, thetitanium nitride layer 13 and Al alloy layer 15 are patterned and areprocessed to form the Al wiring structure shown in FIG. 2D. Then, thesilicon substrate 10, the titanium layer 12, the titanium nitride layer13 and the Al alloy layer 15 are annealed at a temperature of 400°C.-480° C. to reduce the contact resistance between the substrate 10 andthe Al wiring structure.

Furthermore, the insulator film, which serves as the protective film 18,is formed using of CVD or sputtering method at a temperature of 300°C.-480° C. and in doing so, a structure, like the one shown in FIG. 2E,is derived.

During the above annealing at 400-480° C. aimed at reducing theresistance of the electrical connection and during the sputteringprocess at 300-480° C. applied during the formation of the protectivefilm 18, titanium diffuses from the titanium nitride layer 13 into theAl alloy layer 15 and the reactions shown in equations (1) and (2) occurto form the distortion relaxation layer 14. In this case, the distortionrelaxation layer 14, in accordance with the relationship shown in FIG.3, becomes a layer which effectively reduces the number of Al voids withwidths of over 0.3 μm for every wiring width of 1 μm to 0. That is tosay, the distortion relaxation layer 14 becomes a layer which cansuppress the occurrence of Al voids the void width of which are overapproximately one third of the wiring width.

As described above, according to the present embodiment, by forming thedistortion relaxation layer 14, which is an intermetallic compound layerexpressed as TiAl_(x) composed mainly of TiAl₃, in between the titaniumnitride layer 13 and the Al alloy layer 15, the occurrences of Al voidscan be suppressed.

Because the diffusion of titanium from the titanium nitride layer 13into the Al alloy layer 15 for the formation of the distortionrelaxation layer 14 relies heavily on the film quality of titaniumnitride, there are some restrictions in the conditions for the filmformation. The DC power density, which, as stated in the above, affectsthe film quality most, should be set 5.5 W/cm² or less. During the filmformation of the titanium nitride layer 13, it is desirable that theeffective substrate temperature be set at 200-350° C. On the other hand,it must be noted that the bad wettability of the titanium nitrideagainst Al and raising the substrate temperature during the filmformation of Al to over 200° C. make the Al adhere to the inside of thecontact hole 17. Thus, the step coverage of Al might deteriorate andbecause of the fact that the occurrence of Al voids may be linked tosuch bad wettability, it is desirable that the substrate temperatureduring the film formation of Al be set under 200° C., e.g. 100-150° C.Also, because the film formation pressure of the N₂—Ar gas is closelyrelated to the reactivity of the reactive sputter while also affectingthe life span of an exhaust pump, it should be set at 2-7 mTorr. As thegas mixture ratio of N₂ with Ar affects both the reactivity of thereactive sputter and the deposition rate, the partial pressure of N₂ gasshould be set at 33-75%.

Furthermore, in this embodiment, the concentration of oxygen inside thetitanium nitride layer 13, which serves as the barrier layer, is setapproximately below 1 at %, while the oxygen concentration at theinterface of the titanium nitride layer 13 and the distortion relaxationlayer 14 is set at approximately below 1 at %. Because of the above, itis easier for Al and titanium nitride to react to each other and thus,it will be easier to form the distortion relaxation layer 14 with thedesignated thickness.

In this embodiment, the titanium nitride layer 13, which is used in theformation of the distortion relaxation layer 14, acts as a diffusionbarrier layer to prevent Al from diffusing into the Si substrate 10 andalso to prevent Si (from the Si substrate 10) and Ti (from the titaniumlayer 12) from diffusing into the Al alloy layer 15. Instead of theabove, the following structure can also be used: metals with highmelting points, nitride compounds of metals with high melting points,silicide compounds of metals with high melting points or the like, allof which can act as diffusion barrier layers, being inserted between thetitanium nitride layer 13 and titanium layer 12 and/or between thetitanium nitride layer 13 and the titanium silicide layer. Also, inplace of the titanium silicide layer 16 and the titanium layer 12,metals with high melting points, silicide compounds of metals with highmelting points and the like, can also be used.

Also, the Al alloy of the Al alloy layer 15 is not limited only toAl—Si—Cu, but other alloys, i.e. pure Al, Al—Ti—Si, Al—Cu, Al—Si, Al—Ti,Al—Cu—Ti and the like, can also be used.

In addition, the barrier, titanium silicide and titanium layers caneither be multilayered or not. The only vital point, in suppressing Alvoids, is that the Al alloy layer 15 and the titanium nitride layer 13,which is important in the formation of the distortion relaxation layer,are both directly in contact with each other. Besides this, there are noother restrictions on the structure, orientation and the like of thelayers.

(Second Embodiment)

In the first embodiment, explained in the above, the occurrence of Alvoids was suppressed by changing the traditional conditions for formingthe film of the titanium nitride layer 13 and by the formation of thedistortion relaxation layer 14. While this structure made certain thatthe occurrence of Al voids was sufficiently suppressed, there is theproblem that alloy spikes, such as Al spikes, are likely to occur.

An alloy spike is, as shown in FIG. 17, a phenomenon in which the wiringmaterials Al, Ti and Si react to form a compound that badly affects thedevice's characteristics (Tr characteristics). Reflecting on this point,for the conventional method of forming the titanium nitride layer, thepower density during the formation of the titanium nitride layer isrelatively high and after the film formation of the titanium nitridelayer, the film was exposed to the air. While, for this case, theoccurrence of alloy spike was prevented by the relative hardness ofTiN's film, if the power density is lowered, as in the above, to under5.5 W/cm² to suppress the occurrence of Al voids, it can be inferredthat reaction among the metals and silicon substrate is made moreconducive and this results in the occurrence of alloy spike. Therefore,a conflict arises in adjusting the power density because the suppressionof Al voids and the suppression of alloy spike are in a relationshipthat is contradictory to each other.

Thickening the film of the titanium nitride layer can be one way ofsuppressing the occurrence of alloy spike. In other words, by thickeningthe film, the formation of the compound of Al, Ti and Si, which resultsin alloy spike, is suppressed. However, simply thickening the titaniumnitride layer can result in defects in the Al wiring like rupture.

Accordingly, the inventors propose the setting up of an alloy spikepreventive layer, as distinguished from the formation of the titaniumnitride layer which suppressed Al voids, between the titanium nitridelayer (distortion relaxation layer) and the silicon substrate. To put itconcretely, in this structure, a titanium nitride layer 20, havingdifferent characteristics than the titanium nitride layer 13, ispositioned under the titanium nitride layer 13, which suppresses theoccurrences of Al voids and which is in contact with the Al alloy layer.Thus, a two-layered barrier metal structure is formed. The details ofthe second embodiment are explained below.

FIG. 18 shows a cross-sectional view of the wiring electrode of thesecond embodiment. The structure shown in FIG. 18 differs with thestructure shown in FIG. 1 in that the former's barrier structure is atwo-layered structure which includes a titanium nitride layer 13 forforming a distortion relaxation layer and another titanium nitride layer20 for preventing alloy spikes. But aside from this difference, bothembodiments have the same structure. It must be noted here that thereaction layers of the distortion relaxation layer 14, the titaniumsilicide layer 16 and the protective film 18 of FIG. 1 have been omittedin FIG. 18.

The manufacturing process for this structure is explained below. Asshown in FIG. 2B, after forming the contact hole 17 on the interlayerinsulator film 11, the titanium layer 12 and alloy spike preventivelayer 20 are formed, as shown in FIG. 19A, through the same sputteringmethod as in the first embodiment. Then, as shown in FIG. 19B, the Alvoid preventive titanium nitride layer 13 is formed and then, as shownin FIG. 19C, an Al alloy layer 15, made up of Al—Si—Cu, is formed. Itmust be noted here that the same sputtering devices, used in the firstembodiment, are used here and that the films were formed continuouslyinside a vacuum.

Then, as shown in FIGS. 2D and 2E, patterning is performed on theselayers and after annealing than at a temperature of 350-480° C.,preferably at 420° C. or more, the protective film 18 of an insulationfilm is formed thereon. Because of this annealing process, in the sameway as in the first embodiment, the reaction of the titanium nitridelayer 13 and the Al alloy layer 15 results in the diffusion of titaniumfrom the titanium nitride layer 13 to the Al alloy layer 15, therebyforming a distortion relaxation layer (not shown in FIG. 18) at theinterface therebetween.

Here, the conditions for the film formations of the first (underlying)titanium nitride layer 20 and the second (overlying) titanium nitridelayer 13 are shown in Table 1. To make their characteristics different,the first titanium nitride layer 20 was formed at a DC power density of8.7 W/cm² while for the second titanium nitride layer 13, the DC powerdensity was set at 4.4 W/cm². Also, on the thickness of their films, forthe first titanium nitride layer 20, it is 700 Å, while for the secondtitanium nitride layer 13, it is 300 Å, with their total thicknesses setto be 1,000 Å.

The second embodiment is described here by comparing it with theexamples 1-3 for comparison. These examples for comparison have only onetitanium nitride layer and as shown in Table 1, they have been formedunder different DC power densities to make them unique to each other.Also, the thickness of their titanium nitride layers are set to be 1,000Å, to equal the total thickness for the structure stated above that hastwo titanium nitride layers. On the other hand, the thickness of thetitanium and Al alloy layers are set uniformly to 200 Å and 4,500 Å,respectively, for this embodiment and for the examples for comparison.

TABLE 1 Power Ar flow N₂ flow Sub. Density rate rate Pressure TEMP.(W/cm²) (SCCM) (SCCM) (mTorr) (° C.) Second 1st TiN 8.7 90 90 5.5 270Embod- 2nd TiN 4.4 90 90 5.5 270 iment comparative 1 4.4 90 90 5.5 270comparative 2 5.2 90 90 5.5 270 comparative 3 8.7 90 90 5.5 270

Investigation was done on the Al void density and the leakage current ofthis embodiment and of the comparative examples 1-3, the result of whichis shown in FIG. 20. Moreover, for the alloy spikes, investigation wasdone by looking into the leakage current values of the contacts (thenumber of contacts was 1350) using the wiring structure shown in FIG.21. Also, for the Al voids, the number of Al voids for every 1 μm widthand 1 mm long wiring, i.e., the Al void density, was evaluated.

From FIG. 20, it can be seen that while the comparative examples 1 and2, with DC power densities of 4.4 W/cm² and 5.2 W/cm², respectively,suppressed the occurrence of Al voids, it can be inferred that alloyspikes occurred in them because of their large leakage currents. On theother hand, for comparative example 3 which has a DC power density of8.7 W/cm², while the leakage current was small with the occurrence ofthe alloy spike suppressed, Al voids occurred. In this way, thesuppression of Al voids and the suppression of alloy spike run contraryto each other with regards to the adjustment of the power level, and thedetailed manufacturing conditions have to be optimized to satisfy bothusing only one titanium nitride layer. In contrast with the above, forthe second embodiment which has two titanium nitride layers, theoccurrence of Al voids are suppressed by the upper titanium nitridelayer and by the fact that the leakage current is small, the occurrenceof alloy spike is also suppressed easily by the lower titanium nitridelayer.

FIG. 22 shows the results of the XRD (X-ray diffractometry) analysiswhen the DC power density of the mono-layer titanium nitride layer ischanged. From this figure, it can be seen that as the DC power densitybecomes larger, the orientation of TiN(200) changes. Thus, it can beconsidered that this difference in the physical characteristic broughtabout by the change in the orientation greatly contributes to theoccurrences of Al voids and alloy spikes.

FIG. 23 shows the relationship of the DC power density of the mono-layertitanium nitride layer with the leakage current. From this figure, itcan be seen that there is a point of displacement when the DC powerdensity is equal to 6.96 W/cm² such that if the DC power density islarger than this amount, then the leakage current becomes smaller.Therefore, the titanium nitride layer 20 which prevents alloy spikesshould be formed with a DC power density of 6.96 W/cm² or more tosufficiently suppress the occurrence of alloy spike.

Also, after the film formation, the first TiN layer 20 can be formed tohave, for example, a resistivity lower than 200 μΩcm and a relativelyhigher compressive stress above 100 Mpa. Meanwhile, as was explained inthe first embodiment noted above, immediately after the film formation,it is desirable for the second TiN layer 13, which contributes to theformation of the distortion relaxation layer which suppresses theoccurrence of Al voids, to have a resistivity of 180-1,000 μΩcm and afilm stress of 0-90 Mpa.

Next, it will be explained here how the different film formationconditions, as shown in Table 1, bring about different characteristicsfor the same titanium nitride layer. FIGS. 24A and 24B show the resultsof the analysis of the composition, taken along different depths (alongthe depths of the portions were the interlayer insulator film was notformed) with an Auger Electron Spectroscopic device. FIG. 24A shows thecomposition when a titanium layer 12, a titanium nitride layer 20 forthe prevention of alloy spike and an Al layer 15 are formed on top ofthe silicon substrate 10. On the other hand, FIG. 24B shows thecomposition when a titanium layer 12, a titanium nitride layer 13 forthe prevention of Al voids and an Al layer 15 are formed on top of thesilicon substrate 10. From these figures, it can be seen that both havedifferent physical characteristics. Meanwhile, when an Al layer 15 isformed on top of a titanium nitride layer 20, which prevents alloyspike, a thin reaction layer is formed due to the reaction of bothlayers. However, this reaction layer, as stated in the above, is verythin and thus, does not contribute to the suppression of Al voids.

Next, the effects of the thicknesses of the films of the first titaniumnitride layer 20 and the second titanium layer 13 on the leakage currentand the occurrence of Al voids are explained. The results are shown inFIGS. 25 and 26. From these figures, it can be seen that good resultswith the leakage current and the Al voids are achieved even when theratio of the thicknesses of these two layers are changed. Thus, for thetwo titanium nitride layers, even if one of the layers is formed thinly,both layers will still work effectively.

While the same material used in forming the titanium nitride layer 13,which prevents Al voids, was used in forming the titanium nitride layer20, titanium tungsten (TiW), tungsten silicide (WSi_(x)), molybdenumsilicide (MoSi_(x)) can also be used to form the layer for theprevention of alloy spike. However, as in the second embodiment above,if the titanium nitride layer 13 of the same material as the titaniumnitride layer 20 is made, then, both can be made in a continuous processand since their etching processes can be done with the same method, thenthere is the merit of being able to simplify the manufacturing process.

Moreover, while the first and second titanium nitride layers 20 and 13were formed while changing the DC power density during the filmformation of the titanium nitride, the DC power density can also bereduced gradually as the film formation process of the titanium nitrideprogresses. For such case, the sputtering condition must be controlledso that the DC power density at the start of the film formation processshould be above 6.96 W/cm² and that the DC power density at thecompletion of the film formation process should be below 5.5 W/cm².

In addition, it is not necessary for the alloy spike preventive layer 20to be formed continuously with titanium nitride layer 13 that preventsAl voids. Such alloy spike preventive layer can be formed at some placebetween the titanium nitride layer 13 and the silicon substrate 10. Forexample, the titanium layer, the titanium nitride layer (which preventsalloy spike) and the titanium layer, all these three layers, can beplaced in between the silicon substrate 10 and the titanium nitridelayer 13.

While the present invention has been shown and described with referenceto the foregoing preferred embodiments, it will be apparent to thoseskilled in the art that changes in form and detail may be made thereinwithout departing from the scope of the invention as defined in theappended claims.

What is claimed is:
 1. An electrode for a semiconductor device,comprising: a titanium nitride layer; an aluminum wiring layer disposedon the titanium nitride layer; and first and second distortionrelaxation portions including an intermetallic compound of titanium andaluminum, and disposed separately from each other between the titaniumnitride layer and the aluminum wiring layer.
 2. The electrode of claim1, wherein the aluminum wiring layer is made of aluminum alloy includingcopper.
 3. The electrode of claim 1, wherein: an oxide concentrationinside the titanium nitride layer is approximately below 1 at %; and anoxygen concentration at an interface between the titanium nitride layerand each of the first and second distortion relaxation portions isapproximately below 1 at %.
 4. The electrode of claim 1, furthercomprising: a distortion relaxation layer including the first and seconddistortion relaxation portions and disposed at an interface between thetitanium nitride layer and the aluminum wiring layer; wherein thedistortion relaxation layer covers more than 40% of the interface. 5.The electrode of claim 1, wherein the first and second distortionrelaxation portions contain Al₃Ti as the intermetallic compound.
 6. Theelectrode of claim 1, wherein the first and second distortion relaxationportions are formed by a reaction between the titanium nitride layer andthe aluminum wiring layer, at a temperature in a range of 300° C. to480° C.
 7. The electrode of claim 1, further comprising an alloy spikepreventive layer underlying the titanium nitride layer, for preventingalloy spike, the alloy spike preventive layer being made of titaniumnitride but having film characteristics different from that of thetitanium nitride layer.
 8. The electrode of claim 1, further comprising:a substrate having a surface contacting one of the titanium nitridelayer and the aluminum wiring layer; wherein the first and seconddistortion relaxation portions are provided at an interface between thetitanium nitride layer and the aluminum wiring layer, the interfacebeing flat and parallel to the surface of the substrate.
 9. Theelectrode of claim 1, further comprising: a substrate having a surfaceon which the titanium nitride layer and the aluminum wiring layer aredisposed; wherein the first and second distortion relaxation portionsare provided at an interface between the titanium nitride layer and thealuminum wiring layer, the interface being flat and parallel to thesurface of the substrate.
 10. The electrode of claim 1, wherein aresistivity of the titanium nitride layer is in a range of 180 μΩcm to1000 μΩcm.
 11. The electrode of claim 1, wherein a compression stress ofthe titanium nitride layer is in a range of 0 MPa to 90 MPa.
 12. Anelectrode for a semiconductor device, comprising: a substrate; and anelectrode member disposed on a surface of the substrate, the electrodemember being composed of a titanium nitride layer, an aluminum wiringlayer adjacent to the titanium nitride layer, and a distortionrelaxation layer provided at an interface between the titanium nitridelayer and the aluminum wiring layer and containing an intermetalliccompound of titanium and aluminum, the distortion relaxation layercovering more than 40% of the interface that is parallel to the surfaceof the substrate.
 13. The electrode of claim 12, wherein the aluminumwiring layer is made of aluminum alloy including copper.
 14. Theelectrode of claim 12, wherein: an oxide concentration inside thetitanium nitride layer is approximately below 1 at %; and an oxygenconcentration at the interface between the titanium nitride layer andthe aluminum wiring layer is approximately below 1 at %.
 15. Theelectrode of claim 12, wherein the distortion relaxation layer containsAl₃Ti as the intermetallic compound.
 16. The electrode of claim 12wherein the distortion relaxation layer is formed by a reaction betweenthe titanium nitride layer and the aluminum wiring layer, at atemperature in a range of 300° C. to 480° C.
 17. The electrode of claim12, wherein the distortion relaxation layer has a thickness of at leastabout 10 nm.
 18. The electrode of claim 12 wherein a resistivity of thetitanium nitride layer is in a range of 180 μΩcm to 1000 μΩcm.
 19. Theelectrode of claim 12, wherein a compression stress of the titaniumnitride layer is in a range of 0 MPa to 90 MPa.
 20. An electrode for asemiconductor device, comprising: a substrate; and an electrode memberdisposed on a surface of the substrate and composed of a titaniumnitride layer, an aluminum wiring layer adjacent to the titanium nitridelayer, and a distortion relaxation layer provided at an interfacebetween the titanium nitride layer and the aluminum wiring layer inparallel with the surface of the substrate, and containing anintermetallic compound of titanium and aluminum, the distortionrelaxation layer having a thickness of at least about 10 nm.
 21. Theelectrode of claim 20, wherein the distortion relaxation layer ispartially provided at the interface so that the titanium nitride layerdirectly contacts the aluminum wiring layer at the interface.
 22. Theelectrode of claim 20, wherein the distortion relaxation layer containsAl₃Ti as the intermetallic compound.
 23. The electrode of claim 20,wherein the aluminum wiring layer is made of aluminum alloy includingcopper.
 24. The electrode of claim 20, wherein: an oxide concentrationinside the titanium nitride layer is approximately below 1 at %; and anoxygen concentration at the interface between the titanium nitride layerand the aluminum wiring layer is approximately below 1 at %.